Floating recycle pan and process for ebullated bed reactors

ABSTRACT

A floating recycle pan and ebullated bed process are provided to control the flow of the feed into and out of the downcomer even while the oil liquid level in the ebullated bed reactor is varied to provide continuous ebullation and enhance the efficiency and yield of the process.

BACKGROUND OF THE INVENTION

This invention relates to resid hydrotreating and, more particularly, toan improved hydrotreating process and novel ebullated bed reactorequipped with a unique floating pan.

In the past, spiraling oil costs, extensive price fluctuations, andartificial output limitations by the cartel of oil producing countries(OPEC) have created instability and uncertainty for net oil consumingcountries, such as the United States, to attain adequate supplies ofhigh-quality, low-sulfur, petroleum crude oil (sweet crude) from SaudiArabia, Nigeria, Norway, and other countries at reasonable prices forconversion into gasoline, fuel oil, and petrochemical feedstocks. In aneffort to stabilize the supply and availability of crude oil atreasonable prices, Amoco Oil Company has developed, constructed, andcommercialized extensive refinery projects to process poorer quality,high-sulfur, petroleum crude oil (sour crude) and demetalate,desulfurize, and hydrocrack resid to produce high-value products, suchas gasoline, distillates, catalytic cracker feed, metallurgical coke,and petrochemical feedstocks. Thus, it is to our country's benefit toprovide for the availability of adequate supplies of gasoline and otherpetroleum products at reasonable prices.

During resid hydrotreating, resid oil (resid) is upgraded with hydrogenand a hydrotreating catalyst in a three-phase equilibrium of oil,catalyst, and gas bubbles to produce more valuable, lower-boiling liquidproducts. In order to increase the efficiency, effectiveness, andprofitability of resid hydrotreating, it is desirable to maximize theconversion of resid to more valuable lower-boiling liquid products.

The extent of conversion of resid to more valuable lower-boiling liquidproducts depends in part on the residence time of the resid in thereactor.

During resid hydrotreating in ebullated bed reactors, an oil feedcomprising oil and hydrogen-rich gases and fresh hydrotreating catalystsare fed and circulated in a vessel. In prior art devices, a stationarytubular downcomer with a stationary (fixed) pan extends upwardly abovean ebullating pump. The ebullating pump circulates the feed upwardly inthe reaction zone of the vessel, expanding the catalyst bed. The liquidlevel therein fluctuates above and below the stationary pan anddowncomer. When the liquid level dips below the top of the stationarypan, the oil feed does not circulate through the pan, downcomer, risers,bubble caps, and the reaction zone which can cause the liquid to becomestagnant and hot spots to build up in the reactor which can bedangerous. Loss of liquid circulation can cause equipment and/orcatalyst damage, require shutdown of the hydrotreating unit, and/orupset downstream equipment.

It is, therefore, desirable to provide an improved hydrotreating processand reactor for increasing the conversion of resid which overcomes most,if not all, of the above problems.

SUMMARY OF THE INVENTION

An improved hydrotreating process and novel ebullated bed reactorequipped with a unique floating pan is provided which is efficient,effective, and economical. Advantageously, they improve product yieldand increase the conversion of resid (resid oil) to more valuablelower-boiling liquid products such as naphtha (gasoline). They furtherenhance profitability by decreasing formation of carbonaceous materials(coke), downtime and frequency of repair of the unit.

The novel ebullated bed reactor has an oil feed line which feeds an oilfeed comprising oil and hydrogen-rich gases into the vessel of thereactor and a fresh catalyst feed line which feeds fresh hydrotreatingcatalyst into the reactor. The feed is circulated in the vessel, and thecatalyst bed is expanded by an ebullating pump located in the lowerportion of the reactor. A tubular downcomer extends generally upwardlyabove the ebullated pump. Desirably, a floating tubular pan is slidablyconnected to the upper portion of the downcomer to facilitate the flowand circulation of the feed into the downcomer.

In the novel hydrotreating process, the hydrotreating catalyst is fedinto an ebullated bed reactor. The ebullated bed reactor is partiallyfilled to a preselected level with a feed comprising oil andhydrogen-rich gases. A tubular pan floats upon the feed generally aboutthe liquid level and at least partially above a downcomer. The feed isthen directed generally downwardly through the pan and downcomer.Concurrently, the oil and hydrogen-rich gas comprising the feed aremixed together in the presence of the catalyst to produce upgraded oil.In order to minimize coke formation in the pan, one or more purge tubescan be provided to inject gases, such as hydrogen-rich gases, about thepan.

A more detailed explanation of the invention is provided in thefollowing description and the appended claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the ebullated bed reactor equippedwith a floating recycle pan in accordance with the present invention;

FIG. 2 is an enlarged partial cross-sectional view thereof, showing insolid line the recycle pan in a lower retracted position and in dottedline the recycle pan in an expanded upper position;

FIG. 3 is an enlarged partial cross-sectional view of the ebullated bedreactor with another embodiment of the floating recycle pan inaccordance with principles of the present invention;

FIGS. 4-6 are enlarged partial cross-sectional views of the ebullatedbed reactor with various arrangements of purge lines positioned aboutthe recycle pan; and

FIG. 7 is an enlarged partial cross-sectional view of the ebullated bedreactor with a further embodiment of the floating recycle pan inaccordance with principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The ebullated bed reactor 10, as illustrated in FIG. 1, also sometimesreferred to as an expanded bed reactor, includes an upright elongatedvessel 12 with a lower portion 14 and an upper portion 16. An oil feedline 18, conduit or pipe, feeds an oil feed comprising resid (resid oil)and hydrogen-rich gases into the lower portion 14 of the reaction zone20 of the vessel 12. The top surface of the feed in the reactor isreferred to as the liquid level 22. A catalyst feed line, conduit orpipe 24 feeds fresh hydrotreating catalyst into the upper portion 16 ofthe reaction zone 20 to form a catalyst bed 26 in the vessel 12. Thecatalyst bed 26 is expandable from a settled bed level 28 to an expandedcatalyst bed level 30. The upgraded oil produced in the reactor 10 iswithdrawn through the product withdrawal line 25.

The catalyst can be carried through the feed line 24 with gas oil. Aspent catalyst withdrawal line, conduit or pipe 32 withdraws spentcatalyst from the lower portion 14 of the vessel 12. The oil slurriedhydrotreating catalyst enhances the flexibility of the ebullated bedreactors and permits the addition or withdrawal of oil/catalyst slurrywithout taking the reactors offstream. Daily catalyst replacementresults in a steady state equilibrium catalyst activity.

Ebullated bed reactors have many advantages over fixed bed reactors.They permit operation at higher average temperatures. They permit theaddition and withdrawal of catalyst without necessitating shutdown. Theyavoid plugging due to dirty feed and formation of solids during residconversion. And they may be operated at extremely high temperatures andhigh pressure.

Since the liquid resid feed does not usually have enough velocity toexpand the catalyst bed above its settled level, liquid is recycled fromthe top of the reactor to the bottom of the reactor through a downcomerpipe 42 and then pumped back up through the reactor 10 at a sufficientvelocity to attain the required degree of expansion.

The products produced from the resid hydrotreating units in theebullated bed reactors include light hydrocarbon gases, light naphtha,intermediate naphtha, heavy naphtha, light distillate, mid-distillate,light gas oil, vacuum naphtha, light vacuum gas oil, heavy vacuum gasoil, and hydrotreated vacuum resid. Light and intermediate naphthas canbe sent to a vapor recovery unit for use as gasoline blending stocks andreformer feed. Heavy naphtha can be sent to the reformer to producegasoline. The mid-distillate oil is useful for producing diesel fuel andfurnace oil, as well as for conveying and/or cooling the spent catalyst.Light and heavy vacuum gas oils and light gas oil are useful asfeedstock for a catalytic cracker. The vacuum resid can be sent tocokers to produce coke.

An ebullating pump 34 is located in the lower portion 14 of the vessel12, for controlling, expanding and varying the height of the catalystbed 26 as well as for circulating and expanding the oil feed.

The lower portion 14 of the reactor includes a bottom section 35 with ahorizontal distributor plate 36 which separates the reaction zone 20from the bottom section 35 of the reactor. The distributor plate 36 hasa multitude of bubble caps 38 and risers 40 which direct the flow of oiland hydrogen-rich gases upward to the reaction zone 20, while preventingflow of catalyst downward to the bottom section 35.

An elongated stationary tubular downcomer 42 extends generally upwardabove the ebullating pump 34. The downcomer has an upper end portion 44and a lower end portion 46. The upper end portion 44 of the tubulardowncomer 42 also has an inner surface 48 and outer surface 50. Thelower end portion 46 has a flared neck 49 and reduced diameter bottomsection 51.

Referring to FIG. 2, a vertically movable floating annular recycle pan52 facilitates and controls the flow of the liquid into the downcomer 42either when the height of the liquid level 22 is varied or constant. Therecycle pan 52 is fabricated out of a metal, such as aluminum orstainless steel, which resists corrosion from the oil feed, gases andproducts produced in the reactor and which substantially maintains itsstructural integrity and strength at hydrotreating conditions. The panis designed and/or comprises a material which is lighter, less dense,and/or has a specific gravity less than the oil feed so that the panwill at least partially float about the liquid level on the oil feedcontained in the ebullated bed reactor 10.

The recycle pan 52 (FIG. 2) has an inner circular feed passageway 53 andis generally funnel-shaped and has a substantially circular upright wall54 with a top portion 56 and bottom portion 58. The middle of the pan 52has a sloping section 60 comprising an annular inwardly slopingfrustoconical flared wall extending downwardly at an angle ofinclination from the bottom portion 58 of the upright wall 54. Thebottom 62 of the sloping wall 60 has a shoulder 64. An inner annularneck 66 and an outer sleeve 68 or skirt extends vertically downwardlyfrom the shoulder 64. The outer sleeve 68 is sufficiently spaced fromthe inner neck 66 and cooperates with the shoulder 64 to define a pocket70 for slidably engaging the upper end portion 44 of the downcomer 42.The recycle pan 52 is telescopically movable from a lower retractedposition L seated upon the upper end portion 44 of the downcomer 42, asshown in solid line in FIG. 2, to an upper expanded position U with theshoulder 64 spaced above the upper end portion 44 of the downcomer 42when the catalyst bed 26 is expanded, as shown in dotted line FIG. 2.The inner neck 66 of the recycle pan 52 slides upon and engages theinner surface 48 of the stationary downcomer 42. Similarly, the outersleeve 68 of the recycle pan 52 slides upon and engages the outersurface 50 of the downcomer 42. This arrangement allows verticalmovement and facilitates flotation of the recycle pan 52 at leastpartially above the liquid level 22 of the oil feed.

Referring to FIG. 4, an elongated purge line, tube or injector 76 can beused to feed hydrogen-rich gases in and about the pocket 70 between theinner neck 66 and the outer sleeve 68 to substantially minimize theaccumulation of carbonaceous residue in and about pocket 70. The purgeline 76 has an upper vertical portion 77 with an outlet 78 locatedbetween the inner neck 66 and the inner surface 48 of the downcomer 42.

The purge line, tube or injector 79 of FIG. 5 is similar structurallyand functionally to the purge line, tube or injector 76 of FIG. 4,except the upper vertical portion 81 of the purge line 79 is locatedbetween the outer sleeve 68 and the outer surface 50 of the downcomer42.

In the embodiment of FIG. 6, two similar purge lines, tubes or injectors76 and 79 are shown. The upper vertical portion 77 of one of the purgelines 76 is located between the inner neck 66 and the inner surface 48of the downcomer 42. The upper vertical portion 81 of the other purgeline 79 is located between the outer sleeve 68 and the outer surface 50of the downcomer 42.

As shown in FIG. 1, the ebullated bed reactor 10 can have a horizontalbar 80 attached to the inner wall in the upper portion 14 of the vessel12. The horizontal bar 80 is spaced a fixed distance above the top edgeof the upright wall 54 of the recycle pan 52 to provide a stopper or anabutment stop. The bar 80 restricts the distance the recycle pan 52travels above the upper end portion 44 of the stationary downcomer 42when the recycle pan 52 is in the upper expanded position U (FIG. 2) andthe catalyst bed 26 and oil feed are expanded. When the recycle pan 52is restricted by the stopper 80, the liquid level can rise substantiallyabove the top of the recycle pan.

Alternatively, a horizontal pin or bolt 82, as illustrated in FIG. 3,can be attached through a slotted portion 83 of the inner neck 66 andouter sleeve 68 of the recycle pan 52 and the upper end portion 44 ofthe downcomer to provide a stopper or abutment stop. The pin can be heldin place at both ends by nuts, c-clamps or other fasteners. The stopperof FIG. 3 serves the same function as the stopper of FIG. 1 and thereactor operates in a similar manner.

As illustrated in FIG. 3, the floating recycle pan 52 can have anarcuate chamber 84 which provides a fluid pocket or annular cavity inthe outer sleeve 68. The arcuate chamber is spaced radially outwardly ofthe pocket 70 and is preferably circular. If desired, the chamber 84 cancomprise one or more arcuate segments. The arcuate chamber 84 may befilled with a fluid, such as an inert gas comprising nitrogen, hydrogen,and light hydrocarbon gases (methane, ethane, etc.). The fluid can alsocomprise light oils. In order to enhance the flotation and buoyancy ofthe recycle pan 52, the fluid injected and contained in the chamber 84is lighter, less dense and has a lower specific gravity than the oilfeed in the ebullated bed reactor 10.

The embodiment of FIG. 7 is similar structurally and functionally to theembodiment of FIG. 3, except that the chamber 84 contains a solidflotation material 86 which is lighter, less dense and has a lowerspecific gravity than the oil feed in the ebullated bed reactor in orderto enhance the flotation and buoyancy and specific gravity of thefloating recycle pan 52. Preferably, the solid material in the chamber84 of FIG. 7 provides a flotation device. The flotation device enhancesthe stability, rigidity, strength, buoyancy and flotation of thefloating recycle pan 52. If desired, the solid or composite material cancomprise carbon composites, graphite, coke (carbonaceous material),light metal alloys, ceramics and/or plastics. Other materials can alsobe used. The solid or composite material can also be used with thefluids previously described in the embodiment of FIG. 3 and/or can bereinforced with metal.

In order to use the hydrotreating process equipped with the novelfloating pan 52 (FIG. 1), a hydrotreating catalyst is fed through thecatalyst feed line 24 into the reaction zone 20 of the ebullated bedreactor 10 to form a catalyst bed 26. Then, the ebullated bed reactor 10is substantially filled to a preselected height with a liquid level 22below the top of the vessel 12. This is accomplished by feeding an oiland gas feed comprising resid oil and hydrogen-rich gases to the vessel12 through the feed line 18. The resid oil can be diluted with gas oilor other diluents.

Thereafter, the oil and hydrogen-rich gases from the oil feed line 18(FIG. 1) are ebullated, mixed and reacted in the reactor 10 with eachother together with and in the presence of the hydrotreating catalyst,from the fresh catalyst feed line 24, under hydrotreating conditions toproduce upgraded oil. Typical hydrotreating conditions include: ahydrotreating temperature ranging from about 700° F. to about 850° F., ahydrotreating total pressure ranging from about 2,550 psia to about3,050 psia, a hydrogen partial pressure ranging from about 1,600 psia toabout 2,300 psia, and a liquid hourly space velocity (LHSV) from about0.15 to about 0.7 hr⁻¹.

During hydrotreating, the liquid level 22 (FIG. 1) of the oil feed isexpanded and varied in the vessel 12 while, simultaneously, the heightof the catalyst bed 26 is expanded.

At least an upper portion of the generally funnel-shaped annular recyclepan 52 telescopically slides and floats, about the liquid level 22,along the upper end portion 44 of the elongated stationary (fixed)upright downcomer 42 so that the top or upper edge of the upright wall54 of the recycle pan 52 is positioned slightly below the liquid level22 to receive the oil and gas feed. The pan 52 rises in response to anincrease in the liquid level 22 and falls in response to a decrease inthe liquid level 22, for facilitating the flow of feed into thedowncomer 42 in response to the expansion and variation of the liquidlevel 22 in the reactor 10.

Concurrently, the oil and gas feed is circulated, directed and passed,generally downwardly, through the central circular passageway 53(FIG. 1) of the floating recycle pan 52 through the stationary downcomer42 in the vessel 12 by the ebullating pump 34. The oil and gas feed inthe bottom section 35 of the vessel 12, in proximity to the ebullatingpump 34, is circulated upwardly through the distributor plate 36 by wayof a multiplicity of bubble-caps 38 and risers 40 which help to evenlydistribute the oil and the gas across the reaction zone 20. The upgradedoil from the ebullated bed reactor 10 is withdrawn through the productwithdrawal line 25.

Purge gases, such as hydrogen-rich gases, can be injected through atleast one purge line 76 and/or 79 into or in proximity of the pocket 70of the recycle pan 52, as seen in FIGS. 4, 5 and 6, to substantiallyminimize the accumulation of carbonaceous residue or coke therein sothat the recycle pan 52 will not bond, stick or adhere to the downcomer42 and be prevented from sliding and floating.

Although embodiments of this invention have been shown and described, itis to be understood that various modifications and substitutions, aswell as rearrangements and combinations of process steps and equipment,can be made by those skilled in the art without departing from the novelspirit and scope of this invention.

What is claimed is:
 1. A hydrotreating process, comprising the stepsof:feeding a hydrotreating catalyst into an ebullated bed reactor;partially filling said ebullated bed reactor to a level defining aliquid level below the top of said reactor with a feed comprising oiland hydrogen-rich gases; raising said level of said feed by activatingan ebullating pump and concurrently ebullating, contacting, and mixingsaid feed with said catalysts; floating a tubular pan upon said feedpartially below said level in said reactor and at least partially abovea downcomer to allow said pan to rise in response to said rising of saidliquid level for facilitating flow of said feed to said downcomer;directing said feed substantially downwardly through said pan and saiddowncomer in said ebullated bed reactor; and mixing and contacting saidoil and said hydrogen-rich gases with said catalyst to producehydrotreated oil.
 2. A hydrotreating process in accordance with claim 1further comprising injecting hydrogen-rich gases in a pocket in said panfor substantially minimizing coke in said pocket.
 3. A hydrotreatingprocess, comprising the steps of:conveying a hydrotreating catalyst intoa reaction zone of an ebullated bed reactor to form a catalyst bed;substantially filling said ebullated bed reactor to a height defining aliquid level below the top of said reactor with a feed comprising oiland hydrogen-rich gases; ebullating and contacting said feed with saidcatalyst under hydrotreating conditions to produce hydro-treated oilwhile expanding the height of said catalyst bed; expanding and varyingthe maximum height of said liquid level in said reactor; substantiallyvertically moving at least a portion of an annular pan, substantiallyalong an upper portion of a stationary upright downcomer to allow saidpan to rise and fall in response to said variation of said liquid level,said pan having a shoulder, an upright annular neck and outer sleeveextending downwardly from said shoulder, said neck being spaced fromsaid sleeve and cooperating with said shoulder to define a pocket;funneling said feed, substantially downwardly, through said pan and asubstantial portion of said stationary downcomer in said ebullated bedreactor; and withdrawing said hydrotreated oil from said ebullated bedreactor.
 4. A hydrotreating process comprising the steps of:conveying ahydrotreating catalyst into a reaction zone of an ebullated bed reactorto form a catalyst bed; substantially filling said ebullated bed reactorto a height defining a liquid level below the top of said reactor withan oil feed comprising resid oil and hydrogen-rich gases; ebullating andcontacting said oil feed with said catalyst under hydrotreatingconditions to produce hydro-treated oil; expanding and varying themaximum height of said liquid level in said reactor and simultaneouslyexpanding the height of said catalyst bed; floating at least a portionof a substantially funnel-shaped, annular pan along an upper portion ofan elongated stationary upright downcomer to allow said pan to rise inresponse to an increase in said liquid level in said reactor and fall inresponse to a decrease in said liquid level in said reactor so as tofacilitate the flow of said feed into said downcomer in response to saidexpansion and variation of said liquid level in said reactor, said panhaving a shoulder, an upright annular neck and an outer sleeve extendingdownwardly from said shoulder, said neck being spaced from said sleeveand cooperating with said shoulder to define a pocket; circulating saidfeed, substantially downwardly, through said pan and a substantialportion of said stationary downcomer in said ebullated bed reactor;withdrawing said hydrotreated oil from said ebullated bed reactor; andinjecting hydrogen-rich gases into said pocket with at least one purgeline to substantially minimize the formation and accumulation ofcarbonaceous residue in said pocket.
 5. A hydrotreating process inaccordance with claim 4 wherein said hydrogen-rich gases are injectedbetween said sleeve of said pan and said downcomer.
 6. A hydrotreatingprocess in accordance with claim 4 wherein said hydrogen-rich gases areinjected between said neck of said pan and said downcomer and betweensaid sleeve of said pan and said downcomer.